This invention relates to nuclear reactors and it has particular relationship to control and removal of the impurities which accumulate in the coolant of a nuclear reactor. This application deals specifically with nuclear reactors whose coolant is liquid metal, but the adaptation of this invention or its principles to reactors of other types or other coolants is regarded as within the scope of equivalents of this invention.
Typical of liquid metal reactors is the liquid-metal fast-breeder reactor (LMFBR) in which sodium is the coolant. Typically, in such reactors, the liquid metal is circulated through the core between a higher-pressure plenum from which "cold" sodium enters the core and a lower-pressure plenum into which the heated sodium passes from the core. The sodium in the higher-pressure plenum is at about 750.degree. F. and the sodium in the lower-pressure plenum is at about 950.degree. F. The operation takes place in a sealed pressure-tight vessel but oxides, hydroxides and other compounds are generated by the reaction of the highly reactive sodium predominantly with oxygen and hydrogen existing in the vessel as a result of corrosion, leakage and diffusion of air and water vapor, and with the absorbed oxygen and moisture on new equipment, such as the original fuel assemblies and fuel assemblies inserted in the core during refueling. In accordance with the teachings of the prior art, control of these impurities is accomplished by cold trapping. In this prior art practice, the sodium is processed separately by a so-called economizer and a cold trap which is called a crystallizer. The economizer is a tube having a cooling jacket through which sodium from the cold trap flows. The sodium from the reactor inlet (high pressure) is passed through the economizer and then through the cold trap, where it is cooled to a low temperature precipitating the impurities as their saturation temperatures are reached. Then this cooled sodium is passed through the jacket of the economizer where it precools the sodium which passes into the economizer and the sodium stream is reheated before discharge to the reactor outlet plenum (low pressure).
The above-described prior-art apparatus has a relatively short effective life and must be replaced during the life cycle of the reactor. Replacement of this apparatus is costly and requires shut-down of the reactor.
In lieu of the economizer and crystallizer, a so-called getter trap has been proposed. In a getter trap, the oxygen and hydrogen impurities are removed from the coolant by an iron-vanadium-zirconium alloy. This practice is costly because the iron-vanadium-zirconium alloy is costly.
It is an object of this invention to overcome the drawbacks of the prior art and to control and reduce the impurities in the coolant of a nuclear reactor at a reasonable cost and without repeated shut-down of the reactor.